A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle is equipped with a navigation function. Such a navigation system detects the position of the user or user's vehicle, and reads out map data pertaining to an area at the current vehicle position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), or a hard disc. Alternatively, such map data can be provided to the user from a remote navigation server through a communication network such as Internet.
When a destination is set, the navigation system starts a route guidance function for setting a guided route from the start point to the destination. During the route guidance, the navigation system reads the nodes data from the data storage medium such as DVD and successively stores the nodes data of road segments constituting the guided route in a map memory. In the actual traveling, the node series stored in the map memory is searched for a portion of the guided route to be displayed, and a portion of the guided route is highlighted to be clearly distinguished from other routes. When the vehicle is within a predetermined distance of an intersection it is approaching, an enlarged or highlighted intersection diagram with an arrow indicating the direction in which the vehicle is to turn at the intersection is displayed to inform the user of the street and direction to turn at the intersection. Typically, such route guidance is also given by voice instruction.
FIGS. 1A-1H show a typical example of overall procedure and screen display involved in the navigation system. FIG. 1A shows an example of locator map screen of the navigation system when the destination is not specified. Typically, the navigation system displays a street on which the vehicle (current vehicle position VP) is running on a map image and a name of the street. Other information such as a north pointer NP, a map scale and a current time may also be illustrated on the display screen.
An example of process for specifying a destination in the navigation system through a Point of Interest (POI) search method is shown in FIG. 1B-1F. A main menu screen such as shown in FIG. 1B displays menu items including a “Destination” menu for entering the destination. When selecting “Destination”, the navigation system displays a “Find Destination by” screen as shown in FIG. 1C for specifying an input method for selecting the destination. The “Find Destination By” screen lists various methods for selecting the destination including “Address” for specifying the city and address of the destination, “Intersection” for specifying the names of two streets which intersect with one another, and “Point of Interest (POI)” for selecting the programmed destination based on the name, category or telephone number.
When selecting, the “Point of Interest” method in FIG. 1C, the navigation system displays selection methods of point of interest (POI) either by “Place Name” or “Place Type” in FIG. 1D. The “Place Name” is to specify a name of POI, and the “Place Type” is to specify a category of POI. If the “Place Type” is selected in FIG. 1D, the navigation system lists categories of POIs as shown in FIG. 1E. The user selects a desired category of POIs from the lists.
FIG. 1F shows a screen when the user has selected a “Fast Foods” category in the example of FIG. 1E. In this example, the screen includes a list of names of the fast food restaurants typically sorted by distance from the current position of the user. The user selects a particular fast food restaurant from the list. In FIG. 1G, the navigation system calculates a route to the destination. After determining the route, the navigation system starts the route guidance as shown in FIG. 1H. Typically, the navigation system shows the intersection that is highlighted to show the next turn and a direction of the turn.
The navigation system noted above, however, cannot successfully provide the need of a user who wants to visit two or more places, typically, POIs (points of interest), with one stop of a car or a least number of stops. Such a need arises when a user is handicapped, or is traveling with a handicapped person, a baby, or an elder person, etc. In other instance, a user may want to visit two or more POIs with a minimum length of travel, or a user may want to specify an order of arriving the destinations such as a last destination to visit.
FIG. 2 is a schematic diagram showing a map image for explaining a situation where the user wants to reach three destinations. For explanation purposes, it is assumed that a location mark “A” represents an ATM, a location mark “B” represents a pizza shop, and a location mark “C” represents a supermarket. A reference number 57 indicates a current vehicle (user) position and equidistance circles are illustrated on the map image around the current vehicle position 57.
The user wants to take out some cash, eat pizza for a lunch, and shop at a supermarket. The user does not care which ATM, pizza shop, or supermarket to visit as long as the user can accomplish the purposes by making the trip. Thus, there are many candidate locations for each category of places. If the user wants to visit an ATM, pizza eatery, and supermarket in that order, there are several choices. In a conventional navigation system, the first destination that is nearest to the present location is normally selected first, then the second destination that is nearest to the first destination, and then to third destination that is nearest to the second destination.
In FIG. 2, if the navigation system is to use the conventional multiple POI search method, a guided route 1 will first direct the user to a location 1A (ATM), then to a location 1B (pizza), and finally to a location 1C (supermarket). However, although the location 1A is nearest to the present user position and the location 1B is relatively close to the location 1A, the location 1C is far away from the location 1B. As a result, the overall distance for the trip can be long.
In many cases, it is desirable to produce a guided route 2 that first directs the user to a location 2A, then to a location 2B, and finally to a location 2C even if the first destination 2A is located farther from the current position 57 than the location 1A. This is because the overall travel distance to reach all the destinations is shorter in the route 2 than the first route 1.
Even if the travel distance is the same or even longer, in many cases, the user prefers to stop the car as less as possible. That is, it is desirable that the user can accomplish the objectives of the trip at one location by one stop of the vehicle. In FIG. 2, POI locations 3A, 3B and 3C exist within a small area so that the user can visit all of them by one stop of a car. Although an overall travel distance of a route 3 is longer than that of the route 2, the user often prefers the route 3 because it relieves burdens of repeatedly riding and moving the vehicle.
For example, the user is relieved from the stress of finding a parking spot at each destination. Further, if a user is handicapped, or is traveling with a handicapped person using a wheelchair, the route 3 can minimize the trouble of getting on and off the vehicle. Moreover, the one-stop method can benefit people with children who has to load and unload a baby carriage each time the destination is reached. Thus, there is a need of a navigation system that has a function to find a one-stop location, and if no one-stop location is found, to find the most efficient route with the shortest overall distance, or a route that can accomplish the order of arrival desired by the user.